The present invention relates to a method for injection-molding a propeller fan and, in particular, to a method for injection-molding a plastics propeller fan for use in an air conditioner condenser""s cooling fan, ventilator, vehicle radiator""s cooling fan, etc.
Conventionally, a fan as shown in FIGS. 3 and 4 is known as a plastics propeller fan. Here, FIG. 3 is a plan view and FIG. 4 is a cross-sectional view taken along line IVxe2x80x94IV in FIG. 3, that is, shows a blade profile.
Conventionally, this kind of propeller fan has been used for the air conditioner condenser""s cooling fan, ventilator, vehicle radiator""s cooling fan, etc., and has been manufactured mainly using a plastics material.
The blade profile has often been formed with the use of a thin sheet and, in order to improve its aerodynamic characteristics, it is considered effective to use a fan blade having a cross-section as shown in FIG. 4. In this case, however, its cross-section includes a thicker portion.
FIG. 5 shows a conventional mold structure for injection-molding a plastics propeller fan. In FIG. 5, reference numeral 1 shows a mold having a fixed-side mold section 2 and a movable-side mold section 3. By the fixed-side mold section 2 and movable-side mold section 3 a mold cavity 8 is so defined as to conform to a fan as a product. The fixed-side mold section 1 has an inlet 4 for pouring a molten plastics material and a bushing 6 holding a pouring control pin 5 to allow it to be smoothly moved. That is, the pouring control pin 5 is so provided as to extend in the fixed-side mold section 2 and movable-side mold section 3 to allow the control pin 5 which controls the pouring of a molten plastics to be moved in a direction of an arrow A in FIG. 5. A knock-out pin 7 is provided at the movable-side metal section 3 to push out a molded fan from the mold. A knock-out pin 7 is moved in a direction of an arrow B. It is to be noted that the movable-side mold section 3, pouring control pin 5 and knock-out pin 7 have their positional movements controlled by corresponding drive sources.
A thicker blade profile, being thinner in its peripheral edge portion and thicker in its central and base portions, involves an increased weight, shrinkage and increased cycle time in a general injection-molding process, thus presenting the problem of lowering its moldability and incurring added cost.
Although a foam molding, a blow molding, etc., methods are known as the method for obtaining a good thicker molded product, but it has been difficult to obtain a uniform molded product because it is poor in shape accuracy and lower in strength and durability and there is a shrinkage speed difference between a thicker portion and a remaining portion. These result in an increase in amount of unbalance conducive to the rotation variation of the fan.
The object of the present invention is to provide a method for injection-molding a propeller fan comprising the steps of providing a movable core at an area corresponding to a thicker portion of a blade section of a propeller fan; after a predetermined amount of plastics material has been injected into a blade space of a mold cavity defined by a fixed-side mold section, movable-side mold section and movable core and conforming to the propeller shaft, pushing out the movable core into the mold cavity; and, after this step, bringing the movable core back to a normal position conforming to a mold shape defining the blade space and forming a propeller shaft, whereby less weight difference can be achieved between a thicker portion and a thinner portion and it is possible to mass-produce uniform molded articles and it is also possible to lower an amount of unbalance conducive to the propeller fan""s rotation vibration.
Further, another object of the present invention is to provide a method for projection molding a propeller fan which comprises the steps of providing a movable core at an area corresponding to a thicker portion of a blade section of a propeller fan; after the movable.core has been pushed out into a blade space of a mold cavity defined by a fixed-side mold section, movable-side mold section and movable core and conforming to the propeller fan, pressure injecting a plastics material into the mold cavity to allow the material to be filled in the mold cavity; after this step, bringing the movable core back to a normal position conforming to a mold shape defining the blade space and forming a propeller fan, whereby it is possible to obtain uniform molded products and to lower an amount of unbalance involved.
According to a first invention, a method for injection-molding a plastics propeller fan by using the fixed-side mold section and movable-side mold section comprises the steps of providing a movable core at an area corresponding to a thicker portion of a blade section of the propeller fan; after a predetermined amount of plastics material has been injected into a blade space of a mold cavity defined by the fixed-side mold section, movable-side mold section and movable core, pushing out the movable core into the mold cavity; after this step, bringing the movable core back to a normal position (a pre-moving position) conforming to a mold shape defining the blade space and forming a propeller fan. It is, therefore, possible to achieve less weight difference between a thinner portion and a thicker portion and to mass-produce uniform articles. It is also possible to provide a propeller fan which can maintain an unbalance amount conducive to the fan""s rotation vibration lower.
According to the second invention, a method for projection: molding a plastics propeller fan by using a fixed-side mold section and movable-side mold section comprises the steps of providing a movable core at an area corresponding to a thicker portion of a blade section of the propeller fan; after the movable core has been pushed into a blade space of a mold cavity defined by the fixed-side mold section, movable-side mold section and movable core and conforming to the propeller fan, pressure-injecting a plastics material into the mold cavity to allow the plastics material to be filled in the mold cavity; and, after this step, bringing the movable core back to a normal position (a pre-moving position) conforming to the blade space and forming propeller fan. It is, therefore, possible to provide a propeller fan which, as in the case of the first invention, can obtain uniform articles and lower an amount of unbalance involved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.